Formation fluids including oil and gas produced at a well head are conveyed through flow lines to remote gathering stations. It is conventional practice to use safety valves which are responsive to a number of different changes in operating conditions to automatically shut off flow at the onset of unusual or unscheduled operating conditions. For example, conventional oil and gas gathering systems include safety valves which are designed to automatically close in the event of fluctuations either above or below predetermined settings, such as high and low liquid levels, high and low temperatures, and electrical power loss. Also, catastrophic failures may occur in which flow lines are broken by explosion, storm damage and the like, creating sudden decreases in flow line pressure.
It is desirable to be able to completely close off flow in the event of damage or breakage of the flow line to prevent waste of the well fluids or environmetal contamination. Moreover, it is desirable to be able to shut off flow if the pressure in the flow line rises above a predetermined level for any reason, such as an increase in well pressure or a downstream blockage in the flow conductor. In many such operations, the production fluids are conveyed under high pressure from a well which is in a relatively inaccessible location, such as a platform over a body of water or which may become inaccessible due to weather conditions.